Anchor device for steel reinforcing cables



T. GJERDE 3,422,592

ANCHOR DEVICE FOR STEEL REINFORCING CABLES Jan. 21, 1969 Filed Feb. 7, 1967 TV MW? FIGA United States Patent 3,422,592 ANCHOR DEVICE FOR STEEL REINFORCING CABLES Trygve Gjerde, Baerum, Norway, assignor to A/S Stormbull, Oslo, Norway Filed Feb. 7, 1967, Ser. No. 614,508 Claims priority, applicationzlglorway, Feb. 9, 1966,

US. Cl. 52-704 Claims Int. Cl. E04b 1/41; E04c 5/12; E04c 3/26 ABSTRACT OF THE DISCLOSURE An anchor device for the ends of steel reinforcing cables in which the cables are received in a sleeve and are engaged at longitudinally spaced locations in the regions of its ends such that the cables are deformed along an outwardly arched course between the engaged locations. The sleeve is filled with a settable mass which hardens and engages the cables.

The present invention relates to a new embodiment of an anchor device for tension members in prestressed concrete, particularly for tension members of the wire cable type. More particularly the invention relates to a new embodiment of a socket anchor device for securing the ends of high strength wire cable and the like, to provide an anchor head.

The invention shall hereafter be described in connection with tension members in the shape of steel wire cables, but it shall be understood that the invention can be realized with other kinds of tension members, for example with steel wire strands or relatively thin steel rods.

Building structures of prestressed concrete can be produced in various known ways. In the production of building elements in prestressed concrete in a factory, i.e. prefabrication, the tension steel members are tensioned, for example between tension blocks or in special stretching benches straddling the moulds and the concrete is poured into the moulds, the tension stress in the tension steel being transmitted to the concrete mass by bending between the steel and concrete when the concrete has attained about 70% of its 28 day strength.

When prestressed concrete is made on the building site however, it is usually not practical to work with special tension blocks or tension benches, and instead there has been developed a technique whereby the tensioning of the tension steel is delayed until the poured concrete mass has attained a rigidity of about 70% of its 28 day strength, such that the concrete mass itself can form the necessary abutment for a jack device, the gripping means of which is connected to the outer end of the steel members. The tension steel is suitably extended through the concrete mass through channels which, subsequent to the tensioning, are filled with cement grouting which becomes imbedded in the concrete mass together with the tension steels.

On each end of the tension steel members is connected a so-called primary anchor which must be brought into firm and intimate contact with the surrounding concrete mass before the tension stress exerted in the steel by the jack is removed. In order to carry this out, it is usual to provide a tube-shaped or conically shaped recess in the concrete mass around the outer end or ends of the steel on each side of the concrete structure in question, which recesses are filled completely with cement grouting or other high compressive strength binding mass, such that the primary anchor secured on the tension steel is moulded into the concrete (injection anchoring).

There are several different known types of primary anchors, but all of these have their limitations.

3,422,592 Patented Jan. 21, 1969 "ice The main object of the present invention is to provide an improved primary anchor, particularly for steel wire cables and the like, which possesses improved strength characteristics, high reliability and is simple and quick to assemble at the building site.

The anchor device in accordance with the invention is used for securing the ends of parallel tension steel members, particularly steel wire cables, and comprises a socket including a tubular sleeve having a central axis and opposite ends, and a plug secured in said sleeve at one of said ends, said plug being provided with apertures through which the steel reinforcing members pass with the ends thereof terminating inside the sleeve in spaced relation with the other end of the sleeve, an outwardly tapered block in said sleeve, said block being disposed between the reinforcing members proximate said ends thereof, a clamping ring positioned around the reinforcing members outside the block and cooperating therewith to exert pressure on the reinforcing members and cause the reinforcing members to assume an outwardly arched course between the block and plug relative to the axis through the sleeve, and high compressive strength material filling said sleeve and surrounding the reinforcing members and in intimate contact therewith.

With such an anchoring of the steel wires in the socket, the tension stresses in the wire cables are uniformly transferred to and received by the filling material, the stresses thereafter being transmitted as radial or partly radial stresses in the binding mass and from the binding mass to the socket and the plug therein. The stress pattern in the socket will furthermore be such that the tensile stresses in the cables result in an increased bonding force between the cables and the binding mass, and furthermore a wedging effect is produced in the binding mass between the arched courses of the steel cables. The wire cables will, however, simultaneously also be kept in the socket due to the so-called Hoyer-efr'ect, i.e. the cables will possess no stresses at all on the outside or at the end where the cross-sectional area is zero while the stresses will increase uniformly in direction inwardly toward the plug. The cross-sectional area of the steel in the wire cables will therefore decrease in direction inwardly subject to deformation, a fact which results in the formation of radial stresses which again provide great frictional forces and consequent resistance to displacement between the wire cable material and the surrounding mass.

The invention will now be described in connection with the accompanying drawing where:

FIG. 1 is a central longitudinal section through a ready assembled primary anchor in accordance with the invention,

FIG. 2 is a cross-sectional view taken along line IIII of FIG. 1,

FIG. 3 is a sectional view through a prestressed concrete building structure, illustrating the anchor devices in accordance with the invention, the primary anchor shown on the left side of the figure corresponding to the anchor shown in FIGS. 1 and 2, and which is transferring the power directly to the surrounding mass, in other words injection anchoring, while the primary anchor shown on the right side of the figure is transferring the power or stresses via a secondary anchor having a nut and an anchor plate.

FIG. 4 is a longitudinal section view similar to that of FIG. 1 of a modified embodiment of the invention.

FIG. 5 is a cross sectional view taken along line V-V in FIG. 1.

In FIG. 1 reference number 2 designates a socket in the form of a tubular sleeve, suitably a part of a steel pipe, surrounding the end portions of tension members 4 which in the illustrated embodiment and constituted by four steel wire cables which are evenly circumferentially spaced about a central axis. At the inner end of the socket, the cables are passed through a plug 6 comprising an externally threaded annular block which is screwed into corresponding internal threads 8 in the socket 2. The plug 6, disregarding the apertures 10 for the passage of members 4, is provided with a closed cross-sectional area. The inside face of the plug is recessed and provided with an inwardly diverging opening face 12 as shown in FIG. 1. A block 16 is positioned a short distance inwardly of the outer extremities 14 of the steel cable. The block is doubly tapered and receives the cables on its periphery and around this block and the four cables is positioned an annular clamping ring 18, whereby the cables are clamped and pressed together on that portion of the tapered block having the smallest diameter. Each of the wire sections in the socket is thereby pressed radially outwards such that they attain a waved or arch-shaped course 20 such as shown. The end portions 22 of each of the cables are forced outwardly to a substantially curved course as shown.

The assembly of the anchor is suitably carried out in this way. Firstly the cables are slipped through the respective apertures 10 in the plug which has beforehand been screwed into the socket 2. The socket with the plug is then slipped along the cables until the ends of same extend a sizable distance out of the opening 24. Now the cables are bunted together and the tapered member 16 is put between the cables. The clamping ring 18 is slipped over the ends of the cables and the clamping ring is clamped together for instance by means of a tangential tightening screw 19 (FIG. The cables will thereby be pressed against the portion of the tapered block which has reduced diameter with the result that the wire sections 20 are forced apart and are given a diverging course. Then the socket is forced back towards the ends of the cables until the clamping members are in the socket such as shown in FIG. 1. This operation can be carried out by hand and the result is that the cable sections in the socket will attain a waved or outwardly arched course such as shown in FIG. 1.

In an alternative manner of assembling the anchor, only the plug 6 is initially slipped on to the cables, the tapered member and the clamping ring are then placed on the cables in the correct spaced position, and from plug 6 thereafter the socket is slipped over the cables and screwed into the plug.

The socket is thereafter filled completely, preferablyby injection, with a high compressive strength binding mass 25, for instance an epoxy-resin-type, steel plastic or the like, to cover the cables completely as shown. When the mass is hardened the anchor is ready for use.

It will be understood that the type and the number of the steel wires, for instance 2, 3, 4 in number or more, can be varied in accordance with the need. But at least two cables must be present if the primary anchor in accordance with the invention shall give the desired effect. It is furthermore to be understood that the plug 6 need not necessarily have a conical inside face as shown, since the main purpose of the plug is to keep the cables correctly positioned to obtain the wave-shaped curvature as shown. However, a conical inside face on the plug has the advantage that there is created an outwardly directed radial pressure against the socket via the binding mass when the steel members are tensioned, which contributes to keep the plug and thereby the steel members firmly in the socket.

It should furthermore be noted that the tapered member need not necessarily be of double conical shape as shown and can, by way of example, consist of a simple cone 33, such as shown in FIGURE 4, which acts in combination with a clamp ring 35 placed around the bunt of cables. A double tapered block is preferred, however, because the assembly is simplified.

In order to increase the adhesion between the steel cables and the binding mass, one can beforehand apply in the socket and on the cables an epoxy-resin etc., which also can be mixed with metal particles or the like. The inside of the socket can furthermore be provided with threads all the way through to form a very rough inside surface.

On the presupposition that the tension steel cables placed through the poured concrete mass are provided with primary anchors as shown in FIGURE 1 or FIG- URE 4, then the next job will be to mould these cables in tensioned condition into the concrete mass. This can be carried out in a known fashion, in which the primary anchor socket placed at one end of the steel cables, the right side shown in FIGURE 3, is provided with an anchor plate 29 fastened with an outside nut. On the anchor socket at the other end is screwed a spindle 31 on a jack being used to provide the tension, whereafter the cables with the anchors are subjected to the desired stress. Cement grouting or mortar is injected under pressure into the clearance 30, so that the channel 34 surrounding the cables and the enlargements 36 and 38 about the anchor sockets are filled. Thereafter the end openings are closed. When the grouting has hardened the pull in the spindle 31 is released and thereby the concrete mass will receive and balance the tension stress. The anchor plate 29 can be removed subsequent to the grouting injection.

While preferred embodiments of the invention have been described in some detail, and certain modifications have been suggested, it will be understood that numerous changes may be made without departing from the general principles and the scope of the invention.

I claim:

1. An anchor device for securing the ends of a plurality of parallel reinforcing members, said device comprising a socket including a tubular sleeve having a central axis and opposite ends, and a plug secured in said sleeve at one of said ends, said plug being provided with apertures through which the reinforcing members pass with the ends thereof terminating inside the sleeve in spaced relation with the other end of the sleeve, an outwardly tapered block in said sleeve, said block being disposed between the reinforcing members proximate said ends thereof, a clamping ring positioned around the reinforcing members outside the block and cooperating therewith to exert pressure on the reinforcing members and cause the reinforcing members to assume an outwardly arched course between the block and plug relative to the axis through the sleeve, and high compressive strength material filling said sleeve and surrounding the reinforcing members and in intimate contact therewith.

2. A device in accordance with claim 1 wherein said apertures are uniformly spaced in symmetrical relation relative to said axis, and said reinforcing members are in uniformly spaced circumferential arrangement on said block.

3. A device in accordance with claim 1 comprising thread means on said socket and plug threadably engaging the same together.

4. A device in accordance with claim 1 wherein said plug has an inner surface extending into the sleeve beyond said apertures for supporting the reinforcing members, said surface outwardly diverging from said apertures.

5. A device in accordance with claim 1 wherein said block is of double tapered conical shape converging towards its center and said clamping ring is disposed around the center of the double tapered conical shape block.

References Cited UNITED STATES PATENTS (Other references on following page) 5 FOREIGN PATENTS 76,504 11/ 1954 Netherlands.

81,804 6/ 1956 Netherlands.

1,381,003 10/ 1964 France.

HENRY C. SUTHERLAND, Primary Examiner.

JAMES L. RIDGILL, JR., Assistant Examiner.

US. Cl. X.R. 

